The present invention relates in general to devices which provide for the selective adjustment and positioning of movable structural components relative to one another. As will be seen, the device is ideally suited for use in furniture, particularly office furniture, where the current market emphasis on ergonomic design calls for adjustable furniture structures such as used with certain chairs that can be adjustably positioned to fit different individuals with various height, weight and job tasks.
Primarily the device is intended for the positioning of components where frictional locking means is sufficient and load forces are moderate, such as chair arms and back uprights. Here the device can be advantageously used to laterally position the arms so as to accommodate users of different body widths.
In the prior art, chair arm lateral adjustment has been accomplished by means of structural members or "J-bars" provided with elongated slots and bolted to the undercarriage or seat pan of the chair. Adjustment was generally accomplished by reaching under the chair with a specialized tool or wrench and loosening and tightening several bolts. This is a very time consuming operation and cannot be accomplished by the chair occupant while seated, often necessitating the intervention of a maintenance crew. In situations where the same chair is used by several shifts it is often the case that occupants find it difficult to sit comfortably since adjustment of the chair between shifts is generally not possible.
The device and object of the present invention provides for the quick manual positioning and changing of one structural component relative to another. In particular, where office chairs are concerned, the device may serve to laterally position chair arms relative to a chair seat at any of an infinity number of positions within a predetermined range. It will appear clear from the subsequent specification that the device is not limited to use in chairs and articles of furniture but in any use where reliable and economical structural adjustment is sought. In a chair, the mechanism comprises a first shoulder bolt which is threaded on one end with a common thread and on the other end a strong fast-advance thread is used such as an acme thread. A second shoulder bolt is also used which is threaded with a common thread on one end and has a hex head on the opposite end. These shoulder bolts are installed at a predetermined distance from each other with the shoulders in sliding contact with the sides of an elongated slot in the structural element of the chair arm. These bolts are threadably attached to a fixed component such as on the underside of the chair seat or to an adapter plate thereon (pre-installed) to provide a flat surface on the underside of the chair for sliding of the chair arm structural member therealong. A spring disk, known as a Belleville washer, is located on the second shoulder bolt against the chair arm structural member. The lengths of the bolt shoulders are sufficient to allow for free sliding motion of the chair arm member relative to the bolts. Therefore, the Belleville washer is selected so that the second shoulder bolt necessarily compresses said Belleville washer when the bolt is completely inserted (tightened). The compression of the Belleville washer causes the chair arm structural member to remain in sliding, yet firm contact with the underside of the chair or adapter plate and prevents excessive play between the surfaces. A fast advance or acme thread nut is made integral with a lever arm and its threads engage the corresponding threads of the first shoulder bolt. The first shoulder bolt is threadably joined to the adapter plate or chair undercarriage and is prevented from loosening by a lock nut or other suitable means, in such a way that, rotating the lever arm acme nut in one direction increases the friction while rotating the lever arm acme nut in a second opposite direction decreases the friction between the chair arm member and the undercarriage of the chair. Thus, it is possible to operate said lever arm nut while remaining seated on the chair by simply rotating the lever arm from one position to the other. The positions of the lever arm are limited by virtue of the design of the lever arm, which surrounds the head of the second shoulder bolt within an elongated c-shaped slot so that the head of the shoulder bolt limits the travel of the lever arm to the ends of said c-shaped slot. When the lever arm is in the position that causes the greatest friction between the chair arm structural member and the chair undercarriage (fixed component) the device is in the "locked" position and lateral displacement of the chair arm relative to the chair seat is prevented. The opposite is true when the lever arm is in the position that causes least friction between the chair arm structural member and the chair undercarriage because the mechanism is "unlocked", and lateral displacement of the chair arm relative to the chair seat is easily accomplished by manual effort.
The advantages of the device are numerous since it is possible for the chair occupant to remain seated while adjusting the lateral positions of the chair arms and can accomplish this without the use of specialized tools or help from maintenance crews. Furthermore the device is simple to manufacture and install, and by virtue of its geometry can operate with any size of chair arm structural members or arm uprights. The device is also easy to partially conceal under the chair where it does not interfere with normal use of the chair.